Gravitational Definition and 1000 Threads

Hello PF members, Source of the gravitational field in the Einstein field equations is energy–momentum tensor and the curvature of space-time is directly related to the energy and momentum of whatever matter and radiation are present. Suppose a electron at rest . 1- Can this electron be...

Homework Statement Suppose an object of length “l” is located a distance “r” from a gravitating object of mass “M.” From physics you will learn that the gravitational acceleration is GM/r^2. Derive the difference in gravitational acceleration between distance “r” and distance “r+l” from the...

I'm trying to write a class for the gravitational field of any planet (I tested it with values for Earth though), and it gives completely the wrong answer! I suspect this is either a mathematical error, or an issue with my declarations of stuff as public, private, static etc. Compiles, just...

What happens to a body experiencing a gravitational wave? Suppose I put a ball in the path of a GR wave. As the wave passes through it, the space will expand and contract. This means that the space between every point in the ball should expand and contract. But what will be the reference point I...

Is this the correct plot of gravity and motion? x(t) = x0 + v0 t + 1/2 a t^2 F = G m1 m2 / r^2 x(t) = x0 + v0 t + t^2 / (x2 - x(t))^2

Hey guys, take a look at this question if you may Suppose the moon, instead of a sphere, is a disc orbitating the Earth ( the moon's total mass is equal to the disc's total mass), the intern radius of the disc is equal to half the distnce between moon and Earth's center of mass and the external...

Hey guys! What would be the gravitational effect of Earth on it's surface, if somehow the density of mass was uniform and equal to 2/5 of the real value? Assuming that the size e shape os the planet doesn't change.

Hi guys! What would happen to objects on the Earth's surface if it SLOWLY stopped spinning and Earth's gravitational field was kept as always. Thx

If gravitational lens can "focus" light, is it possible with gravitation, so that the resulting gravitation would be strangely unhomogenous? (If it is a dumb/noob question just tell we pls.)

Acceleration due to gravity is used as a constant throughout the massive body,but it varies due to height and depth & also varies from equator to pole,so it affect the rotational speed of planet from equator to pole.So, why would it takes as a constant.

In the absence of a sense of scale, will the gravitational fields of large objects be indistinguishable, one from the other?

Hi all, Thanks for taking your time to help me. It means a lot! For some context: I'm a physics student taking an analytical chemistry course and am a bit confused by the concept of electrical potential. Gravitational potential is the potential energy per unit mass, V(gravitational) = U/m. (I...

I know once the escape velocity is reached, the object will continuous to move away from the Earth. But the Earth's gravity can still act on the object no matter how far it goes, so what keeps the object from stopping or even returning back to Earth? Thanks in advance!

Homework Statement Two basketballs, each of mass 0.58 kg and radius0.12 m, are placed on a floor so that they touch each other. Two golf balls, each of mass 0.045 kg and radius 22 mm, are placed on a table so that they touch each other. What is the ratio of the gravitational force exerted by...

I think I have a layman's understanding of time and length contraction. However, I don't really understand gravitational time delay or distance contraction. If we were to put two clocks at the front and end of a rocket, the one on the top would experience time more quickly than would the one on...

On Wolfram Alpha, I get the following values for gravitational acceleration on Earth due to the sun and moon, respectively: gravitational constant * mass of sun / (distance to sun)^2 → 0.005991 m/s2 gravitational constant * mass of moon / (distance to moon)^2 → 3.68×10-5 m/s2 If the...

I'm not sure exactly how to phrase this question, but I was thinking earlier about electromagnetic waves being absorbed by atoms and 'slowing down' the speed of light. Do gravitational waves propagate slower when blocked by, say, a really massive object? In the same way that light slows down...

I'm preparing a poster presentation on the following paper for a physics course: http://t.co/xiCLV7Y0ZH I do not understand how figure 4 tells us about the red/blue shift. Just from the deflections of the peaks of the airy beam, as well as the deformation, how are we able to infer that there is...

Homework Statement By what angle, in seconds of arc, will a plumbline be pulled out of its normal vertical direction by the gravitation attraction of a 10-ton that parks 20 ft away? Do you think that this effect could be detected? Homework Equations I think (G*m1*m2)/r^2 The Attempt at a...

Dear friends! If there are two particles of unequal masses in a system on which there are no external forces.When let free they collide under the influence of gravitation. Should they always collide at CM. If the system were under an external force of uniform gravitational field will the...

1. Homework Statement Calculate the magnitude of the gravitational force between the Earth and a 3.7 kg mass on the surface of the earth. The distance to the center of the Earth from the surface is 6370 km and the mass of the Earth is 5.98·1024. That gave me 36.37 N Calculate the magnitude of...

Hi Everyone, first post here, another enthusiastic amateur I'm afraid so please excuse my general ignorance! I struck me the other day that it should be possible to find an arrangement of large galaxies that would allow light emitting from our galaxy to be bent back towards us. This would give...

When 2 bodies are locked over relatively large distances (like locked Earth and Venus), do they lock, naively speaking, to the position where another's body is seen (delay distance/c is taken into account) or to the position where other body is actually at the moment (because of Relativity of...

I have this question on my practice test that I can't figure out. "Just as one jumps out of a plane what is their gravitational force given that the mass is 70kg." The thing is, for me to use the gravitational force formula I need to masses. The test only has the one. Am I missing something? Am...

I am calculating the energy transfer in two different formulas and they are giving different results. What could be the reason of this difference? I would be grateful if someone tell me what i am missing here. http://s18.postimg.org/o4tknn77d/potential.jpg

Is the phenomenon of gravitational lensing caused due to the particle nature of light or due to its wave nature? If not so, what is the correct explanation?

Hi, I was wondering if there is any need in the theory of relativity for Newton's Gravitational Constant 'G' to remain a fundamental constant. Constant in Coulomb's Law can be expressed in 'c' and 'pi', then why Constant in Newton's Law needs to be a fundamental constant??

Hi everyone I have been told that gravitational lensing affects CMB power spectra (TT, TE, EE) for high values of l (i.e. the least, low peaks on the right, say l>1000). But how? Isn't the effect of the varying gravitational potential along the line of sight the cause of Integrated Sachs-Wolfe...

bcrowell submitted a new PF Insights post How Fast Do Changes in the Gravitational Field Propagate? Continue reading the Original PF Insights Post.

Homework Statement Point charge Q = 4.26 μC is fixed at the origin. Now, point charge q = 4.88 μC is carefully placed directly above it (along the y-axis), and it floats at (0,9.51 cm). Find the mass of q, in kg. Assume: g = 9.803 m/s^2. Homework Equations F=kq1q2/r^2 G=mg probably The...

Homework Statement Why is the gravitational potential energy of a ball a distance r from the center of the Earth negative? Homework Equations U_\text{grav}(r) = - GMm/r [/B] (To me, this makes sense because gravity is an attractive force and bodies will want to minimize the distance between...

I want a better visual model of what Newton's gravitational force formula represents: (G⋅m1⋅m2)/d2 But there are two contradictory things that I'm having trouble reconciling: Multiplying the two masses shows a relationship between the two point sources, but using the area of the sphere to...

I know gravity is a conservative force field and can be treated as such for all intents and purposes, but I was just thinking that in order to show that a vector field is conservative that vector field must be defined everywhere (gravitational force field is not defined at r=0). I was thinking...

Galaxies outside the observable universe are moving away from the Earth faster than the speed of light. As the two bodies move apart, the gravitational force between them should weaken however as the speed of gravity is equal to the speed of light, the gravitational force would not do so. It is...

In the context of a project, I had to solve numerically Poisson equation with cylindrical coordinates. I put here results for z = 0 on a 3D mesh 256x256x256. Below 1 figure representing the final solution (in absolute value) in the case of a galaxy; I use the CGS units for the potential. I...

Homework Statement A stationary object is released from a point P at distance 4R from the centre of the Earth which has radius R and mas M.What is the speed of the object when it hits the Earth's...

So say I had a glass of water on a table ,with the glass filled to the top. The bottom of the glass, the water would have a higher pressure than the top of the glass. This is the concept of hydrostatic pressure etc. But how does GPE fit into all of this? Does the water at the top of the glass...

If there are two masses with the gravitational effect of (say) N and there are two larger masses which are wider apart but with the same gravitational effect of N; is the gravitational effect between the two larger bodies (that are further apart) greater due to the increased distance between them?

In today's Physics ArXiv: New constraints on primordial gravitational waves from Planck 2015. Authors Luca Pagano, Laura Salvati, and Alessandro Melchiorri of the Physics Department and INFN, Universita di Roma. Primordial gravitational waves from the universe exiting Inflation get more and...

Homework Statement A satellite is designed to orbit Earth at an altitude above its surface that will place it in a gravitational field with a strength of 4.5 N/kg. a) Calculate the distance above the surface of Earth at which the satellite must orbit b) Assuming the orbit is circular...

Can anyone tell me where I can find an explanation that only the gravity of the stars inside the orbit of your star is important in a galaxy? Someone told me this and the integration of gravitational effects I did seems to disagree so I wanted to look at what has already been done.

The acceleration of free fall at the equator is not equal to the acceleration of free fall at the poles.explain?

Homework Statement 1. What is the gravitational energy (relative to the unstretched surface of the trampoline) of the 20kg ball at its apex 2.0m above the trampoline 2. What is the kinetic energy of the ball just before impacting the trampoline 3. At maximum stretch at the bottom of the motion...

I know GWs are produced by moving masses, but I can't find an explanation as to why it happens. A system would lose energy to gravitational radiation. Does the radiation get produced spontaneously, or would it be because the mass has to move through space-time which holds it back somewhat...

Hi, I'm wondering how much prior knowledge I would need to get a lot out of this book. I'm considering taking an undergraduate General Relativity course next semester to help me learn parts of this book. I have some basic experience with curvilinear coords/tensor analysis along with a brief...

Timedilation seems clear when you study special relativity and read about the Hafele-Keating experiment. Gravitational redshift seems logical when you assume that light should lose energy when it is leaving a gravitational field. But the two seem to be contradictory to each other. Question 1...

Hello everyone! I have a question concerning the proof of Poisson's equation for a gravitational field. My question is how can i prove that Gauss's Law is independent of the choice of the closed surface surrounding the point mass? Thanks in advance

Is there any credible hard evidence that this equivalence extends to all moving bodies? We accept on good grounds that the apparent mass of moving objects is enhanced by motion, to a measurable degree that increases indefinitely as observed speeds of relative motion approach c. Likewise...

I am trying to understand the formula's for Gravitational Radiation. At one point in the derivation, every source I have seen comes up with Kirchhoff's Formula but they never derive it. They always just say its a well known result from Electromagnetic Radiation. I have been able to determine...

Hi all, I'm interested in the behavior of electric fields in a gravitational shockwave geometry. I'm specifically thinking about gravitational shockwaves due to null shells as discussed, for example, in Dray-'tHooft http://www.sciencedirect.com/science/article/pii/0550321385905255 (available...